JAKARTA (REUTERS) - A fire tore through an overcrowded block in a jail in Indonesia's Banten province in the early hours of Wednesday (Sept 8), killing at least 41 people and injuring dozens, a government spokesman and media reports said.

The fire, which broke out around 1am to 2am at the Tangerang Prison Block C, has been extinguished and the authorities were still evacuating the facility, said Ms Rika Aprianti, a spokesman of the prison department of the Law and Human Rights Ministry.

"The cause is under investigation," she said.

The block housed inmates being held for drug-related offences and had a capacity for 122 people, she said.

She did not say how many people were present when the fire broke out, but confirmed the jail was overcrowded.

Two foreign nationals were among the 41 inmates killed, according to the country's law and human rights minister.

Minister Yasonna Laoly told a news conference the foreigners were from South Africa and Portugal.

The prison in Tangerang, an industrial and manufacturing hub near Jakarta, housed more than 2,000 inmates, far more than its 600 people capacity, according to government data as of September.

Cells were locked at the time, the minister said, but with the fire raging uncontrollably, "some rooms couldn't be opened." Earlier on Wednesday, Rika Aprianti, a spokeswoman for the ministry's prison department, said 122 were being detained on drug-related offences in a block built to hold 38.

On Wednesday morning local TV showed footage of flames engulfing the detention facility, and later, the building's charred remains as victims were pulled from the scene in orange body bags.

Dr. Hilwani from Tangerang General Hospital told Reuters that some of the bodies had been so badly burned they were unidentifiable.

"The initial suspicion is this was because of an electrical short circuit," police spokesman Yusri Yunus told Metro TV, which cited a police report saying that 73 people also had light injuries.

The electrical wiring at the prison had not been upgraded since 1972 when the prison was built, minister Yasonna told Wednesday's briefing.

Leopold Sudaryono, a criminologist and PhD candidate at the Australian National University, said that overcrowding also complicated emergency evacuation efforts.

"At the Tangerang prison there are only five guards working one shift to guard a prison with 2,079 people" he said. "So fire detection efforts and evacuations are difficult."

The head of the prison was not immediately available for comment on the ratio of inmates to guards, nor the capacity of the facility.

Prison department spokeswoman Rika told local media that 13 guards had been on duty at the facility at the time of the blaze.